A title I always find funny is "Lunar and Planetary Science", as though the Moon is the sole non-planet to be discussed in this context. Either it should be called "Lunar and Ganymedian and Mirandan and ... [...] ... and Cometary and Planetary Science" or the lunacy of listing just ONE exception should be discarded immediately. Why would the term be broad enough to include Saturn's rings, but not the Moon?

I think the simple category error here is the presumption that the question "Who decides" is going to end up having an answer. Who decided how Pittsburgh would be spelled? Who decided that the English definite article was "the"? Who decided that when a group is asked to identify itself, the answer that sounds best is "It's us" rather than "It's we"?

The IAU *happened* to come up with a torturous and counterintuitive definition and they *happened* to make a decision that impacts the textbooks and they *happened*, as Alan notes, to consist more of people who study stars rather than solar system objects. However, the idea went sour at the point that the implication was made that a smoke-filled room owned the term "planet", which provides no service to science for objects in our solar system.

I've registered to watch the debate but I never got any email confirmation. Am I all set? What do I have to do to watch it?

I think the Great Planetary Debate will work itself out over the next several years to decades. And it won't be from a small group in a smoke-filled room, it will be from scientists looking at a much larger dataset (of as-yet undetected and unanalyzed objects) and grouping things according to trends.

A likely example is the historical development of the Periodic Table. From the initial five elements: earth, wind, fire, water, and lifeforce (see avatar), we now have a clear grouping into 118 (and counting) atomic elements. What is very interesting is that early attempts tried to pigeonhole the elements strictly according to atomic mass (law of octaves). It wasn't until Mendeleev ordered elements according to chemical reactivity with guidance from atomic mass that a clear pattern emerged that allowed elements to be systematically grouped.

[Now, what would've happened if the "inert gas" compound XeF2 [CAS# 13709-36-9] had been known back then? Again, there are always exceptions to definitions.]

Years from now, we'll all look back on this and laugh....then get back to work colonizing Titan.

-Mike

Pumpkinpie- I just inquired on your behalf with meeting organizer Hal Weaver. He says you and about 500 of your closest friends who have also registered for the web participation will be getting email info later today answering your particular questions and more.

-Alan

We may need to come to the realization that no one permanently "decides" such things. Students actually learn more from finding out there are multiple schools of thought driven by different interpretations of the same facts. Maybe some discussions need to be left open for now with caveats that things may change as we learn more. No one is teaching there are X number of exoplanets because it is obvious that we are discovering new ones all the time and that the number and types of exoplanets discovered will inevitably keep changing. It's just a suggestion, but maybe the best way for textbooks and educators to approach the planet question is to point to the Dawn and New Horizons missions, which in only seven years will provide us with a whole new set of data on which to base these decisions. Every time we send a mission to another planet, whether a flyby, orbiter, rover, or lander, we discover new things that no one could have anticipated, such as the water vapor in Mercury's very thin atmosphere.

It's just my opinion, but a reversal of the IAU statement that dwarf planets are not planets at all would go a long way in resolving this issue regarding Ceres, Pluto, Eris, MakeMake, and other round KBOs.

I'm going to be attending the GPD in person, and I look forward to a wonderful, tremendous learning opportunity.

I think a lot of this trouble stems from the questionable process by which the IAU adopted the resolution. Waiting until after most of the delegates had left to bring it up created a lot of bad feelings. Not to mention that the definition passed doesn't really make sense. My fear is that this mess might weaken the IAU's role, something that would create chaos.

It does seem to me that Planetary Scientists are the only ones in a position to do such a thing. If there were a consensus around a really solid definition, I'd expect the other IAU members would defer to it.

Maybe it would help to give a special name to the Magic Eight; call them "Classical Planets" for example. Round, isolated, in circular orbits in the ecliptic -- they certainly SEEM special enough to merit special attention.

Things like the moon or Ganymede could be "Secondary Planets". Again, from a Planetary Science point of view, I don't see how any rational definition can leave them out.

Planets that are part of a belt (like Ceres or Pluto) could stay "Dwarf Planets" but those would now be "planets," not minor planets.

Stuff above the meteorite level could be "subplanets" and we'd just retire the term "minor planet".

Probable planets (e.g. fairly bright KBOs) could be called "planetoids" until we had enough data to class them as dwarf planets or subplanets.

I'm still not ready to consider comets to be any kind of subcategory of planet, but I suppose you could "define" comet as an icy subplanet in a highly elliptical orbit etc.

Kids in school would learn the classical planets. Enterprising ones would learn the secondary and dwarf planets on their own.

--Greg

Maybe I'm just belabouring the obvious here, but while some categorisations (e.g., all bodies whose name begins with 'E') are arbitrary, the good categorisatons are those which reflect theory in some way. That's what distinguishes categories such as '>2000km diameter' from 'roundness'. The thing which I guess I find odd is when people find it hard to switch viewpoint, and thus what categorisation is relevant for the discussion at hand. If you want to discuss tectonic features then the roundness criterion is relevant; if you are talking about the way the architecture of the Solar System has been sculpted over time, then orbital dominance is what you want.

Of course, some definitions may be more useful than others for the purpose of knowing which committee gets to name a body, but you'd think that issue could be settled without people crying 'but what about the children'...

I guess I'm saying that I don't think that there's any such thing as an inherent quality of 'planetness' which we can know - that seems a no brainer, put like that, but a lot of the arguments one sees seem to be predicated on something like it. For example, the use of 'what if we discovered...' scenarios.

Now I am told they are getting flooded with extra log in requests for web participation and won't cut off the list until morning. Only then will they send out the instructions, answers to questions, etc.

-Alan

I guess I was more interested than I thought. I signed up to get the webcast.
(Hopefully it'll get through my work's firewall.)

I like your ideas, but I think kids should be taught the dwarf planets and secondary planets too, not necessarily to memorize, but at least to illustrate that they are an important part of the solar system. Even back in the 70s when I was in elementary school, we learned about the larger moons of the planets. Leaving out Titan, the Galilean moons and the dwarf planets seems to me to be doing a disservice to the kids.

I thing the moon versus planet definition works. Even planet-sized moons have histories so intertwined with their parent planet that it separates them from objects in solar orbit (even Triton was melted down in the process of being captured).

I don't know if this would be a good one for the Planetary Society to get caught up in. The debate is to emotional. The Planetary Society is a non-partisan group (and I am referring to sides in scientific debates, not party politics, although that would also be true I guess), and to risk a result that makes it look petty or turns some of the community against it would be dangerous. Also, it is primarily a group that works to advocate the funding needs of Planetary Science in Congress and to educate the public about planetary science and planetary missions. That even includes educating people about what is being debated. But to step into a debate that some might see as an attempt to supplant the IAU and to risk having a position adopted that alienates some of its constituencies doesn't seem worth it.

I'm not sure I would use "arbitrary" and "good" as opposites like this. Many (most?) uses of terminology are "arbitrary" but have managed to avoid the emotionalism and controversy that this one has caused.

If it were up to me, I would have just said that everything Pluto-sized and bigger was a planet and everything smaller wasn't, but somehow this has been dismissed as being too "unscientific".

The whole thing reminds me of the vociferous debate I was involved in about whether longitudes should be positive to the east or west (also horribly confused by the IAU.)

I don't understand what the motive is to create a term (even a reasonable one) for the purpose of singling out a group. If the purpose is to create a cutoff for educators, perhaps. But scientifically, Mars is still more similar to Pluto than it is to Saturn. Your comments above, especially the ones I've quoted, imply that this isn't about science but about providing direction to educators.

I'll point out that elementary school math teachers neither seek nor find direction in cutting-edge research mathematics, showing just how different those two sides of the topic are. Serious academics in mathematics interact with "quotients" all the time, but they aren't any better than your typical fourth-grade math teacher (who likely has forgotten any calculus they ever knew) to determine the nomenclature in an elementary school text. In fact, the math wonks are possibly especially poorly-suited to do that.

But this puts a pinpoint on the divide between the science issue and the educational issue. And I think the shame of it is that while educators should look to researchers for the basic facts (eg, does Venus have volcanoes?), which is an objective matter, this labeling and nomenclature is not an objective matter, and handing the reins to the researchers to help decide what the kiddies will be taught is just going to make people jaded about what scientists do.

As an aside, I have bought a number of books about the planets for my son, and the subtle misinformation that's rampant in most of them tells me that any possible lesson in classifying bodies correctly (if there were a "correctly") is way below the signal-noise ratio as it is.

(Sample misinformation: Venus's thick clouds MAKE its atmosphere dense.)

I taught over 16,000 students in a portable planetarium this year. Part of the show was letting the kids choose where in the solar system to visit. Most classes chose to go to Pluto. When I asked what it "is," close to 100% had at least one person who knew it was a dwarf planet. In most classes I heard a chorus of the correct answer.

Knowing its label, of course, isn't enough. That's just a form of memorization, and has no meaning without explanation. I would talk about why its category changed, and that there are bound to be more additions/subtractions/reclassifications as our knowledge of the solar system changes.

Educators are an interested party, since kids can understand this stuff. Contrast math, where higher math is utterly unintelligible to even a talented undergraduate student -- much less an elementary school kid.

It's not completely frivolous to consider educators. Fascination with the planets is a first step into science for many people.

To recap:

Planetary Scientists (not the Planetary Society!) ought to have first call; this is their field of study, so they have the biggest stake.

The IAU itself needs a criterion for assigning names, and that does need to be based on what can be observed -- not what properties might be observed if only we could send a probe.

But educators inspire the next generation -- both the young scientists and the interested non-scientists who are happy to see their tax dollars spent exploring space. Their needs cannot drive the definition, but any definition certainly needs to take them into account.

--Greg

Yep, kids like superlatives. I felt that way as a kid too. It's hard to beat "furthest away," although I wonder if Jupiter came in second? (Actually I'd guess Saturn, since the rings are unique.) If they knew about Sedna, they might have picked that.

Pleasing the kids isn't the same as educating them, though. All kids know this already. :-)

--Greg

That's an excellent point on several levels; certainly I was first interested in science by the very concept of planets.

I hope that some educators will participate in the GPD. They may bring some perspective to the whole issue by defining concepts that really communicate with people (and, hopefully, not trying to sell a particular viewpoint.) SInce IMHO the whole thing is quite subjective, it might be much more important to make the final result intelligible & teachable.

I would dispute that it is the "correct" answer any more than the law made "Pittsburg" the correct spelling of that city's name.

Age and background are important variables, but I think this Planet Debate -- not just the particular IAU decision, but the debate itself, as it's been transmitted -- is an absolute disaster for primary education. Speaking as a parent who's bought a few books for his son, some of which were updated with impressive speed. For very young kids, the meta-arguments about classification systems are completely incomprehensible. And I have books where the page devoted to Pluto is now half about this issue. This is a shame first because it displaces whatever else could have been said in that half-page. Second, because kids below a certain threshold of grasping abstractions totally miss whatever point could be made beautifully to a student of the philosophy of science. It's like taking an elementary school text about a tropical island with imagery and comments about the weather and diet and replacing them with information about how the local legislature works. For kids who are sufficiently below the level of understanding for that, it doesn't even provide the building blocks of understanding -- it's just 50 seconds of noise, the way a literature lecture in Hungarian would fail to educate a mature English speaker of one iota of the subject matter or Hungarian.

This subject matter near and dear to our hearts gets a limited amount of discussion in the classroom, and this issue only serves to crowd out some of the real content to replace it with opinion presented as fact. With a tinge of pedantry to boot. That's no wins and three losses.

But kids cannot understand the comparative pros and cons of alternative classification systems. Not before about ninth or tenth grade, on average. Younger than that, and a discussion like that will just be noise. And if instead you just give them the IAU definition as fiat, you're passing opinion off as science.

No, it certainly is not frivolous to consider educators. I'd go much further -- this issue is primarily of interest to educators, and has done them the disservice of asking them to accept an arbitrary and divisive definition with the misinformation that it is a scientific truth newly had.

"This" is not Planetary Scientists field of study. As I mentioned before, the class of body that Pluto might be does not inform scientific papers on Pluto, just as papers about Mars do not hinge on Mars being a planet. Research scientists have no stake in this, but have chosen to browbeat educators into accepting a fiat which is not science, shaky classification, and poor education. And this would be equally true if they had (or "will", as they likely will, in time) handed down a definition ruling Pluto to be a planet.

Just to take an arbitrary example of the non-usefulness of this term for scientists, here's a poster/paper about the spectra of Pluto and Charon: http://www.lpi.usra.edu/meetings/acm2008/pdf/8150.pdf

The paper doesn't anywhere use the terms "planet" or "dwarf planet", or any terms for Charon, for that matter. Can we conceive of any way in which such terms could better inform the science, if they were included in this paper? For any proposed definition of "planet"? I sure can't think of one.

In essence, the term has no use for scientists. It has a folk use, like "hill" and "river", and is therefore useful in folk senses, in the classroom. For scientists to call this their field and therefore their term is like the legislature saying that city names are their field and therefore theirs to decide. So it began in Pittsburg and so it ended in Pittsburgh.

It is this argument that I have been most bothered by -- it seems incredibly anti-science to me. But only a planetary scientist can answer it with any authority.

Your Pittsburgh example is poor by the way, since (the way I heard the story) it's the only US city that resisted standardization.

--Greg

That statement baffles me. Axiomatic trust in authority? Scientists have the answers because they are scientists?

In a software company, it's frequently evident that the engineers are not the best people to name things. Just because astronomy is not-for-profit doesn't change that. The engineers know the software best, spending their days hands-deep in it. That does not make them the best ones to lay down the nomenclature, either for internal or external purposes. It's quite a separate thing from the subject matter expertise.

While I would expect to trust scientists first in a scientific matter, this is a nonscientific matter which happens to be attached to objects that science studies. And while one might expect them to have uses for terms they use in their work, I cited the brief paper/abstract on Pluto to show that the term is not essential to science, and I would certainly welcome an example where the term "planet" was helpful to any scientific paper on any solar system object. If it's about Mars, it's about Mars.

And Pittsburgh is not a poor example because it's the only example of a place that resisted the fiat. One, because it's only the largest of several places. (Pittsburgh, KS; Edinburgh, Indiana; Plattsburgh, NY; Newburgh, NY; Newburgh, IN). Two, because the point is that public usage is a force to be reckoned with. If there were no local affection for a particular spelling elsewhere, then it was a one-sided tug-of-war that the authorities won by default. In Pittsburgh, the two went head to head and the authorities lost.

It's too bad the debate tends to fixate on Pluto and whether the dwarf planets should be considered planets. I think the techniques used to decide which of the TNO's are dwarf planets is more interesting. For example, determining how large an object needs to be before it is in hydrostatic equilibrium, and the methods used to estimate the diameters of the objects.

I've seen some claims that an icy body would be in hydrostatic equilibrium if it is over 450 km in diameter. But I've also seen a presentation (IIRC by Tancredi) that used the shape of light curves and some models to estimate the density and roughness of objects which found a couple of objects to be either to rough or not dense enough to be in hydrostatic equilibrium. Some of those objects have been estimated using infrared radiation detected by the Spitzer Space Telescope to be 600-700 km in diameter. It looks like these estimation methods will need to be verified by other methods such as determining the size and shape by observing stars being occulted by the objects.

Biologists classify animals (a cow is still a cow no matter what genus it's in).
Paeleontologicists classify fossils (T-Rex is T-Rex regardless of who you consider its cousins to be).
Librarians classify books (Roving Mars is still Roving Mars if you put it in the science section or the biography section).

Planetary Scientists should classify planets.

You'd think that would be a no-brainer, wouldn't you?

The only caution I'd have is to avoid circularity (!): you define planetary scientists as people who study planets, and then this group defines planets. For example, I would think people would count the study of asteroids and comets under planetary science (though I'd be interested to hear if people think otherwise), and you don't want to end up with a situation where yet more people feel excluded by the outcome of a definitional debate.

That said, the representation at GPD seems encouragingly broad.

Conversely, educators should decide how they will convey the science to the public (and, yes, there will be educators at GPD too - go look at the abstracts), with input, not legislation, from the scientists. I'm surprised more hasn't been made of the idea of a technical definition - for example, a strawberry is not technically a berry, and a shark is not technically a fish, and scientists and the public both seem to live happily with that.

At that point, we enter the realm of utterly pointless semantics. We all know what planetary scientists are. They study the 'things' out there. Earth, Mars, Titan, Pluto etc etc.... the bodies pertinent to the issue in hand. Thus they should be classifying them.

People who study quasars, nebulae, cataclismic variables and so on are not and were not the right body for that.

This is starting to sound like a potential turf war; and like all turf wars it generally all comes down to where you draw the line...and who is entitled to exercise the power to draw those lines.

So "Planetary Scientists should classify planets", eh?

OK, but who gets to decide what is a planet and what isn't (so as to allow planetary scientists to get on with their all-important classification work)? Planetary scientists themselves?

That is to say, do planetary scientists ALONE get to decide not just what a planet is but where the line is between (say) planets and stars. (Eg is a brown dwarf a star or is it a planet?)

On the other hand those who prefer to classify stars (let's call them "starry scientists", "star scientists" for short; after all if you can have "PLANETary scientists"... ) might like to have some kind of a say of their own in that sort of decision. That would, however, raise the question of just how much of say they would be entitled to. Are they only entitled to a say on drawing the line between stars and planets and would then be turfed out of the meeting room when the discussion turned to the line between (say) planets and comets? (Instead the "cometary scientists" would be allowed in and given a say. )

Of course the very line implied above between "planetary scientists", "star scientists", and "cometary scientists"--not to mention "moon scientists", "cometary scientists", and "plutoidary scientists" (let's try to be consistent here! )--raises the issue of just who exactly is a "planetary scientist" anyway?

Higher up this thread somebody (volcanopele) pointed out: "Don't forget that planetary scientists also study moons, asteroids, comets, dwarf planets, Trans-Neptunian Objects, etc. We don't just study planets." That statement could be construed to suggest that a geologist is basically nothing more than a "planetary scientist" who specialises in a single planet: Earth! (And something similar might be said of, "moon science", 'cometary science" etc. ) Or to phrase the matter another way, "planetary science" might be said to be not a branch of geology. Geology (aka "Earth science") is actually a branch of "planetary science"!

On the other hand, is "planetary science" the study of any planet EXCEPT Earth? If so, that would seem to exclude GEOlogists per se from having a say in deciding what exactly is a planet.

======
Stephen

...and a cow with 50% mouse genome is technically no longer a cow(wt) [wt = wild type].



How about we let the term "planet" have the widest possible use? Let everything go in there.

(OK, make a cut somewhere: like "objects composed of normal-generacy atoms at a density > interstellar gas nebula that are not currently undergoing fusion")

That will allow "planetary" scientists to study gas giants, comets, ice giants, moons, rocks, KBO's, etc.
Each paper will need to define the set of comparitive objects de novo: "We compare Pluto with other KBO planets [Sedna, Eris, Makemake,...]"

And educators will have to introduce students to the full wonderful diversity of objects in and beyond our solar system.


Eventually, better definitions will arrive, most likely from the same set of comparitive objects being used in the scientific literature. (Just like the chemical reactivity patterns eventually helped define the Periodic Table).

-Mike

Quite.

Why don't we just accept the geo- prefix as its proper meaning of ground/earth (as opposed to Earth) and call it all geoscience?

"Biologists classify animals" is a good one to look at. First of all, they do so with controversy and alternate approaches of many kinds.
I think George Lakoff laid out a pretty good look at this and how biologists really aren't very good at stepping back and considering the meta-issues of classification, peerless as though their knowledge may be of the DNA and the organs and so on. He has a very good analysis of some of the controversy which I think is very relevant to the planet debate, but is also way too long to copy-paste here.

But I think it's a useful case to look at because there are some similarities, and the biology controversy surrounding the kingdoms is several years further along. And also has relevance for kiddies' textbooks.

One there were two kingdoms in biology: plant and animal. Then three. Then two "empires". Then 4 kingdoms, followed by 5 and by 6. Then three domains. Some of these various systems were refinements of some other, compatible. Sometimes they were incompatible and led to division, name-calling, hair-pulling, etc. We can't rehash all of the drama.

But step back and consider the relationship of this to the children's schoolbooks. At which points in the debate do you shred the previous edition, buy a new one and teach the new classification system as fact? Keep in mind that we're talking about 12 years on average between a new system. And each new system is proposed but not accepted with unanimity. The idea that any of this strikes anyone as a matter of fact is as incomprehensible as someone saying that the child who said that Pluto was a dwarf planet is "correct".

This is all very good stuff for students of the history and philosophy of science -- wonderful tangles of complexity and controversy and elusive truth. But it's horrible subject matter for children 9 years old. They just don't get it. Can't. And lots of the PhDs don't get it either, as Lakoff describes. They get one system or another and live by it as a religion, but they can't see the interrelation of the alternate systems that their colleagues favor.

In some cases, though, there is an important basis in the biological classification of kingdoms. Some tiny critter's genetic tree might depend crucially on some phenotype or genotype. It's controversial, but worth pursuing. There is reason to believe in a light at the end of the tunnel.

For planetary science, the term "planet" isn't even useful -- or I'd like someone to point out how it is useful in discriminating the kinds of bodies we're talking about. A paper on Pluto's spectrum cannot possibly be informed by whether or not the thing cleared its orbit. The definition they've latched onto has nothing to do with what they study.

So the harm in all of this is to take a vote of disputed authority, and promptly rewrite the textbooks and tell the kiddies that we've learned something through science, when science had nothing to do with it. And keep an eye on your watch, because the Whittaker system of biological kingdoms had 8 years before the next one came along, which is even less time than Pittsburgh lost its "h".

Three (or more) issues here:

1. The IAU definition sucks.
2. The IAU lacked authority.
3. 'Planet' could end up being as imprecise a term as 'continent' or as precise a term as 'metal.'

You go in an infinite loop from #3 back to #1 because of the whole "cleared its neighborhood" crapola. So a planet is the biggest thing around? Right, like lakes are bigger than the biggest ponds around. Mountains are bigger than the biggest hills around.

A lot of people are either bothered or not bothered by number 3. With some terminology that predated science, like the word 'metal,' we have been blessed with some rather precise terms. This is generally because they had specific, quantized characteristics, and not relative characteristics. Metals were defined as ductile, shiny, malleable, whatever. They were not defined as less shiny than diamonds and more shiny than rocks. Turns out there is conductivity, electrons, etc, but what is a metal and what is not has been relatively constant.

On the other hand, 'Continent' has somehow not seen obsolescence due to science discovering plate tectonics, even though we now know there is a fault above India and not one between Europe and Asia. So Europe isn't really a continent, and India is??? Try to read wikipedia for a precise definition of 'continent.' It's all about "convention." Try telling every grade school teacher that we now have the continents of Eurasia and India. In my opinion, either way would be fine, but you are just redefining an admittedly imprecise term. The maps of the world on wikipedia's plate tectonics article and wikipedia's continent article do not match. Science doesn't match the pre-existing term, yet it will still adopt it when discussing "supercontinents" and the like. Schools still teach students the continents, even though it's not a precise term.

You can count me as not bothered by #3-- I'd take it either way-- precise, or defined "by convention." But I certainly understand the disgust with the IAU's botched attempt at "precise."

To me the significant point about the biological analogy is that there is not a unique classification system. Classifications as 'top predator', 'predator', etc., or aerial, marine, littoral, etc. are just as valid as the phylogenetic one depending on the kind of investigation one undertakes. But they can be completely cross-cutting. It's easy to kid oneself that the phylogenetic classification is somehow 'real' or at least trumps the others, and that there might be something similar for bodies 'out there'. I don't think it is, and I don't think there is.

A few comments from a microbiologist:
I think there is some confusion between scientific research and authority to define scientific terms.
Progress in science results from experiments where data is generated and analyzed. Hard science deals with measurements and validating hypotheses. However, every field need a vocabulary to communicate within the speciality and to the broader community. The assigning of objects (molecules, bacteria, planets) to groupings has more to do with esthetics than science (but should be scientifically informed). Determining the mass of a virus or planet is a scientific task which we can do with great precision. Coming up with definitions or names depends on building consensus (no standard error bars) among scientists in the field.
In biology, we can determine the evolutionary distance between living organisms by sequencing the DNA for the small ribosomal RNA and counting the mismatches in the aligned sequences. This measurable information is helping to define the grouping of all living organisms (Kingdom, Phylum, Order ...Genus, Species). In microbiology, an international committee validates all names, but microbiologists are free to ignore approved names for what they think is correct. Usage and consensus eventually rule. The scientists responsible for naming grouping and objects in biology do so only for their area of expertise. Zoologists name animals, Botanist name plants and microbiologist name bacteria and archaea. Seems logical to me for planetary scientist to come up with the definition of a planet. Its helpful if the scientific definition does not differ too much from common understanding or general usage (but often it does for good reason).
The IAU definition seem to flunk the esthetics test as well as the consensus of people in the field test.
-Floyd

All of these examples are useful for setting up a classification of Classifications.

"Continent" has three useful candidate definitions.

1) The large, nearly-contiguous landmasses evident on globes. Ignoring the isthmi (there's a word you hadn't seen yet this decade) of Suez and Panama, you have North America, South America, Australia, Africa, Antarctica, and Eurasia. If you're a traveler -- an extreme mountaineer, perhaps -- it's quite useful. Or for setting up international fishing domains or somesuch.

2) The landmasses known to the ancients, augmented with the four discovered later. Same as above, but with Europe and Asia separated.

3) The landmasses whose tectonic plates whose areas are centrally or primarily land instead of sea. That puts India and Arabia on the list, with Eurasia grouping Europe and Asia.

One thing I find obnoxious about the whole planet thing is the presumption that because the people using #3 are scientists that their definition is "The" definition, leaving the PhDs to "tut tut" and stroke their beards kindly in derision, and leaving museum docents to tell the child who "knows" about #3 that he/she is correct and leaving the poor, misinformed kids brought up on literature and culture to sulk in their incorrectness. It's so wrong. It's not only factually wrong; it's immoral.

No one should begrudge geologists the use of #3. It's great for what they're doing. It's useful. It's a happy world where they use it for their purposes without feeling like silly Virgil and the whole Classics department are ignorant because they use #2 and brow-beating the elementary schools of the world into adopting #3 because it's a fact. Although it's great if geology teaches that #3 is useful -- for geology.

Now if scientists had stumbled upon a scientifically useful definition of planet and kept it to the scientific domain without sending out a memo that the silly people are incorrect and ignorant, that would have been fine. But what has happened has deviated from that in three unfortunate ways:

1) The memo has been sent out. Kids who use that definition are told they're correct. Kids who don't aren't.
2) The definition was almost painstakingly crafted to be useless to scientists! Far worse than if geologists had brow-beaten the geographers into submission, this is a case where the scientists have created a definition that ONLY has relevance on the other side of the boundary. The scientists themselves have no use for it.
3) Per my observation of the books I have (unfortunately) bought and taken into my own house, actual scientific content that was present in earlier editions has been eliminated and replaced with this fad. Whatever meager information was once there about Pluto, it's now been cut in half. Instead of telling them that we can use the light from Pluto to tell that it's made of ice, we're telling them something that isn't science.

I think the point is that everyone already knows what it is that Planetary Scientists study. That's not at issue, even a little bit, and with that the rest of your argument collapses.

As for the arguments that others keep making that Planetary Scientists themselves have no use for the term, let me quote Alan Stern from earlier in the thread:



Note that this is the quote that changed my mind.

I also thought of another group who might appreciate a good definition of planet as well as a selection of subcategories. Those would be the scientists who are doing simulations of solar system formation. It could be useful for them to have a better vocabulary to describe what sort of bodies their simulations are generating. I suspect those guys are already Planetary Scientists of some stripe or another, but I'm not sure. Theirs would certainly be a useful voice in the debate, I'd think.

--Greg

Per the term "planetary", it's clear that the field is concerned with things that aren't planets. I believe we can rightly say that some biologists are concerned with things that aren't alive, but that relate to life. Both on macroscopic scales and microscopic. And Saturn's rings aren't even in the ballpark of being anything someone would call a planet. But I don't see why that calls for a definition of planet. A biologist doesn't need a formal definition of "life" before studying proteins. I don't even see why a definition of "life" would be useful before, during, or after someone starts a study of proteins.

The current IAU definition of "planet" does seem to be to have some possible use for dynamicists. As Greg posited, for discussion simulations of planetary system evolution and so on. Although exactly which terms they'd find useful (and why they would want to steal the term "planet" instead of something like "accretion nucleus"), we'd need a dynamicist to say. But I think it would be just as inappropriate to have someone like that create a definition that impinges on elementary school textbooks as it would someone who studies the surface and interior processes of such worlds.

I don't see this, though. There are countless popular terms that don't match the scientific ones, and it doesn't bother anyone. An architect friend once told me that what I call "asphalt" he calls "asphaltic cement," and that for builders, asphalt is just one of the ingredients. Matters a lot if you're a builder, but the general public doesn't care. It's cute to know that a tomato is technically a fruit, not a vegetable, but only a botanist cares. Kids learn about it, but they don't go correcting their parents about it.

Or consider a rock that falls from space. In space, it's a "meteroid" (and presumably an object a Planetary Scientist might want to study), but once it hits the atmosphere, it becomes a "meteor" (perhaps of interest to Meterorologists) :-) and when it hits the ground, it's a meterorite (and belongs to Geology). Normal folks don't know these distinctions (if I've even got them right myself) and they don't care. They just call everything a meteor. A bright kid might correct his elders in a museum -- "That's not a meteor, dad; it's a meteorite!" -- but they just chuckle.

I can't for a minute see how any of this rises to the level of a moral issue. And kids "brought up on literature and culture" simply say "who cares?" They never give the wrong answer in the first place.

--Greg

Yay! Registration came through. And... you can submit questions... Bwahahaha!

In other news, I got my "Instructions for Viewing The Great Planet Debate Webcast" e-mail about an hour ago. So it's tomorrow, starting at 1:30 PM PDT (2030 UT).

--Greg

If there is a room full of kids who are offering answers, and after one of them gives the "asphaltic cement" answer and the docent says "Yes -- correct!", the kids who gave other answers before that, without getting the positive feedback, certainly notice.

And my ideals for education are not a one-child = one-subject delineation where the literature/culture kids have to feel like they're on enemy turf in the science museum, where the science-kid gets his "Yes -- correct!"s for a day. If it's because the science kids actually DOES know a fact (like the Sun being bigger than the planets), then that's great. If it's because of a matter of interpretation that someone's going to pretend is a fact, eg, a geologist saying the geographical definition is wrong, then it's a problem.

If a kid who'd been told that Europe was a continent interacted with someone preaching that the tectonic plates determine the continents, telling the kid that he/she is not correct is not appropriate.

And portraying a vote that went one way as an advance in knowledge and a determination of what's correct is also not appropriate. If it were correct in the conventional sense, this debate wouldn't be taking place.

Not got mine yet.

JRehling It is clear that you don't like the IAU telling everyone (public, educators) that their definition is a new "Scientific truth". I think most people on this forum would agree. Its just a definition which is neither true or false, but rather useful or not or esthetic or not—most would agree that IAU's definition is not great, or we would not be having this discussion. However, at times you seem to imply that arrogant scientists are to blame for confusing the public. I don't think this is the case. I think we should allow the possibility of a disconnect of the general definition of a word from the definition most useful to a scientific discipline. Do you agree that scientist should be free to give very specific definition of words for their specialty as long as they don't put out press releases stating that a simple definition is a "TRUTH". I sort of like the very old definition of a planet as anything that wonders relative the distant stars. Children and the public should be made aware of the fact that there are often multiple definitions--I agree that "right answeres" should generally have more qualifications.
Floyd

I'd be happy if this were a situation where a term had a scientific use and a folk use, and never the two did meet. A wonderful example of that is "work", which has a definition in physics and a definition in ordinary life which is quite different. (Except when a laborer hauls things up a hill, and activity which meets both definitions.) Hopefully, no one was ever lectured that their job wasn't work because it failed to meet the physics definition.

However, this "planet" definition has no apparent scientific use, and is being used to *replace* the way the term was previously used. So it's a total strike-out. It doesn't help science, and it does impact the folk audience (kids, laypeople).

And while I agree that a very astute audience (graduate students in the history and philosophy of science) could really sink their teeth into these distinctions, the books I've bought for my son are aimed at an audience that is struggling to understand how a space rock could create a hole in the surface of a planet. Meta-classification is way too abstruse a subject for them. So the discussion doesn't enrich their education. It replaces a small part of it with static. The same way that replacing a small portion of a kid's book about a small country with a paragraph about their bicameral legislature would be static.

Actually, what constitutes a "metal" to a geologist (or an engineer) is quite different to what an astronomer means by that word!

Which, of course, raises the question of what would happen if the geologists' union decided that they had the right to determine the meaning of the word "metal"? Would astronomers thereafter follow the new "official" definition or would they blithely ignore the dictates of the geologists and continue to use their own idiosyncratic version of the word (namely, that every element but hydrogen and helium is a "metal")?

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Stephen

Some kids might get so confused by all of this that they just decide it's not worth learning and give up on the subject altogether. When thinking of education, we need to focus on how to excite kids about astronomy rather than turn them off to it.

Also, regarding the IAU requirement that an object clear its orbit: wouldn't that preclude any binary planetary systems since two planets orbiting one another would not be considered to have "cleared their orbits"?

1) Actually, I think your argument is that any planet definition is useless, and we've already established that this claim is false. I don't know why you keep repeating it. At this point, you need to get a bona fide Planetary Scientist to make that claim, and I don't think you can find one. Failing that, you should drop it.

2) It does occur to me that a word like "planet" is very different from words like "fruit" or "work" in that the general public has no independent experience with planets, so the scientific definition has to be the only definition. Contrast fruit, where the common definition requires it to be sweet (thus excluding the tomato) or work, where the popular and scientific terms only vaguely match. No one is bothered by this conflict, and scientists are free to redefine either term without much notice from the public.

But for "planet" the only defiinition that matters is the scientific one. The public cannot create its own term, since it has no use for it. Some special term for the eight planets the public can actually see with (at most) binoculars probably makes sense, but even that's weak; almost no one is looking.

Planetary Scientists should define to term to suit themselves, and everyone else should accept their definition. They should give some guidance to educators, perhaps along the lines I've suggested, but that's it. It's just not anyone else's business. (Clearly I have drunk Alan's Kool-Aide to the lees.) :-)

3) It does seem clear that the IAU overstepped. Their real message seems to be that they don't want any more "planets," but their actions sinice suggest they're reserving the "cool" names for bodies large enough to be round. That being the case, since their whole role is assigning names, they're unaffected by any serious proposed definition anyway. I'd argue that removes them as a party with a legitimate interest.

--Greg

Well, for it to rise to a "moral issue," I really think it needs to be so bad that it makes the kids kill their teachers (or vice versa), and I don't think we've seen that yet. :-)

As for the "cleared its orbit" definition, I think I see how that can be cleaned up, but I now think that's the wrong way to go.

--Greg

Do also remember that whatever definition of planet upon which we achieve consensus doesn't only need to account for solar system objects. Such a definition ought also to include bodies orbiting other stars.

I can conceive of a lot of solar systems in which major planets have not (yet) cleared their orbital neighborhoods. Young systems, for example, where accretion is *nearly* finished, or older systems where large planets are migrating closer to, or farther away from, their stars. Or systems in which a hot mega-Jupiter, orbiting its star in two or three days, finally spirals in and hits the Roche limit.

Are all of the bodies in such systems not planets because of these circumstances? Does "planet" only and forever describe only eight bodies in orbit around our Sun, disregarding bodies that are already described as "extrasolar planets"?

Or do we need to get better data on other systems to find out just how many adjustments we need to make to *any* definition of planet based only on our experience of our own solar system?

-the other Doug

FYI the word "planet" (which derives from the Ancient Greek for "wanderer"), and the concept behind it, is a very ancient one. It existed long before science was even thought of, and thus long before the true nature of planets was discovered.

In other words, it was the public not the scientists who first noticed the wandering stars in the heavens and who created both the word and the concept behind it for those "stars". Astronomers and other scientists are merely the johnny-come-latelies who are now making the most use of it!

Why then should it be the scientists alone who now decide what that word means? That would look an awful lot like expropriation, IMHO. That is to say, science would have presumptively taken custody of a public word and decided to dictate to that public what that word should mean.

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Stephen